Archive for May, 2014

Just been told I got today’s Earth Science Picture of the Day (EPOD) http://epod.usra.edu/

Took a look, and yep, sure enough, my favourite insect – the Morpho Rhetenor butterfly which kindly provided me with the Patent design for a new type of Photonic Crystal 🙂

Thank you Jim at EPOD for continuing to publish my work.

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I am getting all the bits together to be able to put another Canon 200mm prime lens on the mini-WASP top plate.  I will use an M26C camera from the top TS80 scope and will put an eyepiece (shock-horror) into the TS80.  I haven’t actually looked through an eyepiece in years.

Goods that have arrived so far:

1)  Canon 200mm f#2.8 prime lens.

2)  Set of beefy scope rings to hold the lens and camera.

3)  Several 72mm – 52mm step-down rings to hold a 52mm IDAS filter in front of the 200mm lens.

4)  A 52mm IDAS filter.

5)  A Geoptik adapter for fitting the 200mm lens to an M26C OSC.

I am making up a pair of Aluminium mounting blocks that go between the scope rings and the top plate.  I will put two mounting holes into the scope rings to prevent twist – they only come with one tapped hole.

I am awaiting delivery of a 4th Paramount counterweight as the 3 that are already on there are right at the bottom of the counterweight shaft, i.e. I can’t put any more weight on top until I get the extra counterweight.

I am also awaiting delivery of a whole bunch of Allen bolts for the scope ring mountings.

So it’s all slowly coming together.  I will also put the Robofocus from the TS80 onto the 200mm lens and see if I can get it autofocusing (I know this is a non-trivial exercise).

As it looks like it will be clear tonight, I have put the 72mm – 52mm step-down adapter on the original 200mm lens and fitted a 52mm IDAS filter.  I set the lens to f#2.8 (i.e. wide open) and I will check yo see if there are any diffraction spikes or not.  If there are still spikes I will put an aperture in the Geoptik to cover whatever part of the lens iris is showing.

Busy, busy 🙂 🙂

 

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Sergi Verdugo is a very clever chap http://astrophoto-sv.com/index.php?p=1_78 🙂

I have been thinking today about setting up a second Canon 200mm lens on the mini-WASP array for the wide field work.  To this end I was looking for 72mm HUTECH IDAS light pollution filters (I have one of these on the Canon 200mm lens I am currently using) and was drawing a blank.  Searching for HUTECH IDAS filters I came across Sergi’s (very nice!) work and found his ingenious solution.

First let’s go to basics and what I did.  I put a 72mm LP filter on the front of the Canon 200mm lens and stopped the lens down (using its internal diaphragm) to f#4.5.  Why did I stop it down?  Two reasons: one so that the filter will work (it is not designed for f#2.8 which is the lens wide open) and secondly so that I get good quality stars across the whole APS-C size sensor.  I also get the 8 highly annoying diffraction spikes around bright stars from the diaphragm thrown in for good measure.

Here comes Sergi’s solution.  Fit a 72mm – 48mm step down adapter to the front of the Canon 200mm lens and put a 48mm IDAS filter in that.  You automatically stop down your lens to f#4 where the filter will work and you will get good star shapes.  In addition you can now work with the diaphragm wide open – so no diffraction spikes – how brilliant is that then?

I bought the 52mm IDAS filter instead of the 48mm, so I get a tiny bit more speed out of the lens, and I bought a 72mm – 52mm step-down adapter from e-Bay.  I already have a 52mm – 48mm step-down adapter, so I can put in my 48mm narrowband filters when I want to do some narrowband work – and all with no diffraction spikes.  How cool is that then?

Thank you very much Sergi, a great solution – and one that I should have come up with years ago – and didn’t.  I guess I’m getting old.

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Here is the current status of the mini-WASP array as of beginning May 2014.  The latest addition is the autofocuser for the Canon 200mm prime lens fitted to the top plate.  So we have:

1)  A Megrez 80 used as a guide scope together with an SX guide camera connected to one of the M26Cs.

2)  A TS80 triplet APO with 48mm IDAS filter and an M26C OSC CCD.

3)  A second TS80 triplet APO with 48mm IDAS filter and an M26C OSC CCD.

4)  A Sky 90 with a 52mm IDAS filter, filter-wheel with H-alpha, H-beta, OIII and SII narrowband filters and an M26C OSC CCD.

5)  A Canon 200mm prime lens with a 72mm IDAS filter and an M26C OSC CCD.

Probably enough for anyone 🙂

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Grabbed a couple of pics of the Tom How autofocuser this afternoon.  Follow the yellow lead from the stepper motor to the control box housing the Arduino and the stepper motor drive board.

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Met up with Tom How for the first time in quite a while and he brought along the stepper motor/Arduino drive unit for auto-focusing the Canon 200mm lens.  Focusmax talks to the unit (and to Maxim DL) and it all looks the business.  Just need to have the top plate off the mini-WASP AGAIN to replace the JMI electric focuser with this stepper and I should be in business.  Yet another quality astronomical product from the Tom How factory 🙂

 

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